Apparatus for holding silicon slices



July 8, 1969 w. D. QUEEN 3,453,783

APPARATUS FOR HOLDING SILICON SLICES Filed June 50, 1966 INVENTORZ l LIAM D. U FIG. 3 WL O EEN ATTORNEY United States Patent 3,453,783 APPARATUS FOR HOLDING SILICON SLICES William D. Queens, Dallas, Tex., assignor to Texas Instruments Incorporated, Dallas, Tex., a corporation of Delaware Filed June 30, 1966, Ser. No. 561,943 Int. Cl. B24b 41/06, /00, 29/00 US. Cl. 51-216 3 Claims ABSTRACT OF THE DISCLOSURE This invention relates to apparatus for holding thin wafers for polishing, and more particularly, but not by way of limitation, to apparatus for holding silicon slices for polishing.

In the manufacture of electronic devices from silicon, it is common to form relatively thin silicon slices which must be polished on at least one face.

A conventional manner of mounting the slices involves affixing the slices to a polishing block by use of cerese wax or beeswax. The metal polishing block on which the slices are to be mounted is first heated by placing the block on a hot plate or the like. When hot, the block is rubber with a solid stick of the wax which melts to form a layer of molten wax. The wafers are dropped onto the molten wax and the block removed from the hot plate to permit the wax to solidify. To assure that the slices are level on the polishing block, a weight is placed on the slices during solidification of the wax. Any wax contacting the top, or exposed face of the slice must be removed with a suitable solvent, such as trichloroethylene. The polishing block may then be inverted and the exposed face of the wafer contacted with a rotating grinder or polisher, or alternatively the slices are rotated and contacted with a stationary grinder or polisher.

Since the slices are relatively thin, in some cases having a thickness of about mils, the wax used to affix them to the polishing block must be very clean since any particles lodging beneath the slice could cause a crack to form during application of the weight or during the grinding and polishing operations destroying the electrical properties of the silicon.

When polishing of the slices has been completed, the polishing block is again placed on a hot plate or the like to remelt the wax to permit removal of the slices. The slices, upon removal and before treatment with doping agents and the like, must be cleaned with a suitable solvent such as trichloroethylene to remove any wax adhering to the slice.

The steps of mounting and demounting the slices are time consuming, manual operations which are quite costly.

The present invention involves apparatus which greatly reduces the time necessary to mount and demount slices which are to be ground and polished. The invention may be generally described as apparatus for holding thin slices so that one face of the slice is exposed for polishing which includes means defining an opening having a configuration within which the slice may be relatively snugly accommodated. An elastomeric member forms with the opening a recess having a depth less than the thickness of the slice, and the elastomeric element is supported in this relationship by suitable means.

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To be more specific, reference is here made to the drawings, in which:

FIGURE 1 is a top plan view of one embodiment of the invention;

FIGURE 2 is a cross-sectional view along line 2-2 of FIGURE 1;

FIGURES 3 is an enlarged cross-sectional view of a portion of the embodiment illustrated in FIGURES 1 and 2; and

FIGURE 4 is a partial top plan view of an alternative embodiment.

With reference to FIGURES l, 2, and 3 a conventional polishing block 4 formed of a cylindrical plate of metal or the like is provided about its periphery with a plurality of teeth 5 adapted to engage a gear, not illustrated, for driving the block. Affixed to the surface of block 4 by an adhesive 6, such as Pliobond brand adhesive, is an elastomeric member which takes the form of rubber pad 7. Rubber pad 7 preferably has a durometer of about 60 and may conveniently be between and inch thick. Affixed to the relatively planar elastomeric surface 10 of pad 7 by an adhesive 8, such as Pliobond brand adhesive, are a plurality of opening defining members, such as annular rings 9. Rings 9 are preferably made of a relatively deformable plastic material such as Mylar film which preferably have a thickness on the order of about 7.5 mils. While a Mylar film is preferred, other relatively deformable plastics and rubbers may be used.

Rings 9 form with pad 7 a plurality of recesses 11 which are adapted to receive, and accommodate relatively snugly, a plurality of silicon slices 12. The depth of recesses 11 is less than that of the thickness of the slices 12 so that faces 13 of the slices are exposed above the rings 9 to prevent contact between a grinding or polishing wheel and rings 9.

Slices 12 may be retained within recesses 11 to permit inversion of the polishing block 4 in the conventional manner by placing a drop of water on the bottom face 14 of the slice. The surface tension of the water will serve to retain the relatively light slices within recesses 11.

With particular reference to FIGURE 3, it will be noted that faces 13 and 14 of the slices 12 are rough before polishing. Pad 7, due to its elastomeric nature, will conform to the irregularities in face 14 preventing the creation of unwanted stresses in slice 12 during polishing. Additionally since the rings 9 are of a relatively deformable plastic, any engagement of the periphery 15 of the slices with rings 9 during polishing will not result in chipping of the perihpery 15 of slice 12.

While the particular embodiment illustrated in FIG- URES 1-3 is the preferred one, it is also contemplated that a plurality of recesses may be drilled in polishing block 4 and an elastomeric member placed in the bottom of the recess to abs-orb the irregularities in faces 14 of slices 12. Preferably, the peripheries of the recesses would be lined with a relatively deformable material to protect the peripheries 15 of the slices during the polishing.

It is also contemplated that rings 9 may be formed of a ferromagnetic metal in which case block 4 could be magnetized and the rings 9 adhered directly to the surface of block 4 by magnetic attraction. An elastomeric pad could then be placed in the bottom of rings 9 and adhered in place by any suitable adhesive.

In the embodiment illustrated in FIGURE 4, the need for the adhesive used in the embodiment shown in FIG- URES 1-3 is eliminated. In FIGURE 4, the polishing block 16 is covered with an elastomeric' pad 17 which in turn is covered by a circular Mylar film 18 having a plurality of apertures 19 which, with pad 17, define recesses 20 adapted to receive silicon slices 12. The elastomeric pad 17 and Mylar film 18 are retained in juxtaposition by a plurality of nuts 21 which are threadably received about a plurality of screws 22 extending through block 16, pad 17 and film 18.

Once the slices 12 illustrated in FIGURES 13 have been polished, they may be removed by flowing water into recesses 11 to float the slices from the recesses 11. The slices 12 illustrated in FIGURE 4 are removed in the same manner.

Because the slices are preferably retained in recesses 11 by use of Water and are demounted by use of Water, the adhesive used in the embodiment illustrated in FIG- URES l-3 is preferably one which will withstand repeated application of Water without deterioration.

While rather specific terms have been used in describing embodiments of the invention, they are not intended nor should they be construed as a limitation on the invention as defined by the claims.

What is claimed is:

1. An apparatus for holding a plurality of thin wafers so that one face of each Wafer is exposed for polishing, comprising:

a block having a planar surface,

an elastomeric sheet affixed to said surface,

and a plurality of annular rings afiixed to said elastomeric sheet within which said wafers may be relatively snugly accommodated,

.4 said rings being of height less than the thickness of said Wafers. 2. The apparatus of claim 1, wherein said annular rings are of a relatively deformable plastic material.

3. The apparatus of claim 1, wherein said annular rings comprise a magnetized ferromagnetic material.

References Cited UNITED STATES PATENTS 1,673,903 6/1928 Cripe 51 216 XR 1,911,221 5/1933 Blair 51-216 2,112,636 3/1938 Sawyer. 2,309,080 1/1'943 Hunt 51-283 x 2,395,700 2/1946 Walker 51 216 2,539,561 1/1951 Wolfskill 51 133 2,632,288 3/1953 Diller 51 237 X 2,736,993 3/1956 Tripp 51 131 2,699,633 1/1955 Lapenas 51 216 HAROLD D. WHITEHEAD, Primary Examiner.

US. Cl. X.R. 51--13l, 237 

